1. Field of the Invention
The invention generally relates to the use of a rare earth/chelating agent complex for digital fluoroscopy, and more particularly to the use, in digital fluoroscopy, of a contrast medium consisting of a non-radioactive composition of a rare earth metal and a chelating agent.
2. Description of Prior Art
Digital fluoroscopy or digital fluorography (DF) is a technique whereby X-ray signals are detected electrooptically and converted into digital forms which can be processed, recorded and displayed. Processing provides a means to remove certain features from the image and enhance other clinically significant structures.
For the diagnosis of vascular diseases, this can be accomplished either by temporal subtraction wherein two images are obtained before and some time after administration of vascular contrasting media and then subtracted, or by energy subtraction wherein images are nearly simultaneously acquired using different energy X-rays, or by a hybrid technique embodying both temporal and energy subtraction processes.
The field of DF is described by a number of synonymous terms including digital radiography, digital subtraction fluoroscopy, computerized fluoroscopy, digital video angiography, digital video subtraction angiography, digital subtraction arteriography, and intravenous video arteriography. DF provides a simpler means for diagnosis of vascular diseases with less patient risk than conventional arteriography or nuclear imaging techniques.
Current techniques of vascular imaging by DF procedures necessitate parenteral administration of large doses of diatrizoate meglumin or related iodinated substances as contrast media (18-30 gm of iodine per 30-50 ml injection), and the ultimate success or failure of the procedure is entirely dependent upon the absence of any patient motion during or between acquisition of the two images. In addition, injection of heavily iodinated contrast substances is associated with definite patient risk, and is accompanied by significant patient discomfort following the procedure.
There is an urgent need, therefore, not only to develop a less toxic contrast material, but also to develop a contrast media, and a method for employing it, that will improve current DF techniques so that patient motion is no longer a problem.
A digital radiography system essentially consists of an X-ray source, X-ray image intensifier, a high quality TV camera whose output is converted into digital format, a digital image processor, and a display. Such a system is disclosed in copending application Ser. No. 300,587 filed on Sept. 9, 1981.
The system provides for increased low contrast capability and shorter acquisition time, compared to conventional diagnostic radiology equipment. Processing systems provide for rapid image construction, and also for flexible options, such as subtraction, multiplication and convolution, that can be designed to increase the clinical potential of the technology.
Two promising processing techniques, temporal subtraction and energy subtraction (both discussed above), are presently being developed for contrast imaging. More attention has been devoted to temporal subtraction processing techniques, wherein images are obtained before and after administration of the contrasting agent, and these images are subtracted to remove underlying or overlying structures from the field of interest.
Iodine-containing compounds are the only type of contrast agent used in human vascular studies using DF. The greatest limitation to this processing method is that there is a finite, and sometimes prolonged, interval between the images obtained prior to and at the peak of contrast. Patient or physiologic movements between exposures occur, and the subtraction image obtained consequently suffers. The technique also requires administration of relatively high doses of contrast agent, which is frequently accompanied by some definite patient risk and discomfort.